Mac Pro fan pulses - is it normal?

The fan in my Mac Pro (new March 2008, not the fan, the system) even though it is very quiet, sometimes makes a kind of pulsing noise. It is not what you would call noisy but it is getting on my nerves as my office is often very quiet, indeed silent.

Install smcfancontrol and raise the fan rpm's to see if it goes away. Am thinking its a harmonic hum coming from your disk drives though but not real sure. If you raise the rpm's and find thats not it, place your hand on top of the pro and press down firmly and see if that does it. My old 2006 mac pro had something like that and found out it was the 4 drives doing this.

Just to add, use istat widget to watch the fan rpm's to see if they are going up and down. When is the last time you blew the dust bunnies out of the pro?

You know, it would be a nice idea if some hardware manufacturer could come up with a desirable solution to in-take air filtering. It might help reduce the amount of dust in our systems. Three weeks ago, I did that house keeping for my two boxes and together both MP's managed to filled my dyson with fur balls!

I had fan noise from my Mac Pro by a curious mishap sometime. I fitted a better fan unit to my 3870 graphics card which ended up having slightly higher fixtures at the back of the card. Now the four nuts holding the fan connected with the metallic RAM cage. It gave me a sound that drove me nuts for a day. I inserted a piece of paper and the noise was gone.

In another instance my main fan unit wasn't fitting correctly. I found out that one of the black labels of the Foxxconn cable set was caught between the logic board socket and the fan unit connector. After clearing the obstacle the fan unit mounted much easier and the noise was gone.

I had a similar "pulsing" noise coming from mine. It turns out its the case itself. If I lift the lever in the back that locks the door on it goes away. I just leave that lever up now. I think it's the hard drives vibrating slightly, causing the case to hit it resonance frequency.

I had a similar "pulsing" noise coming from mine. It turns out its the case itself. If I lift the lever in the back that locks the door on it goes away. I just leave that lever up now. I think it's the hard drives vibrating slightly, causing the case to hit it resonance frequency.

That may not be your problem, but give it a shot.

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When I first bought my Mac Pro, I had 2 hard drives - one in each of the first two bays. When I added a third, I started noticing the pulsating vibration. I searched the forums and found different users posting various remedies, some a ghetto as shoving cut up strips of a towel into their Mac, some more refined, like using rubber washers between the drive and drive sled. I now have all four HDD bays occupied, mounted with rubber washers, and I only occasionally get "the hum" (it kind of worked itself out). A quick bump to the top of the computer (the handle) solves it most days.

OP - Determine whether your problem is the fan or a vibration before messing with the fan speeds.

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